When did you realize it was all single-shot?

At the end of the first scene, with the prisoner, I thought, "I don't think I've seen a cut," but I couldn't be sure. I watched all through the second scene, which I believe was Holly?, and confirmed my suspicion. It was definitely during "Holly" that I became sure that they were all "tracking shots" (how antique a term that's become now that there are steadicams), so if that was the second "life," it was during the first one that I suspected.

I think it's brilliant. I don't think it's necessary to enjoy the film, but it added to my enjoyment, knowing that each take was a single take. I think the pressure must have gotten better performances out of the actors. I think I saw a mistake, and I think you could almost see the actress sort of wait for the director to say "cut," and then go on. It was a near-phrase, and the actress started to say the phrase, and then stopped herself and said the dialogue instead. If I think of it I'll come back and say what it was, but I'll probably have to see it again. I certainly plan to see it again, and maybe again and again.

Unfortunately I learned about it before watching the movie. But after the 3rd life i completely forgot. So well done.

Not until I watched the interview with the filmmakers.

I would like to attribute it to the beauty and flow of the scenes, and that I was so engrossed in the character's stories...

but more than likely I just suck at noticing details. Dammit. :)

Good film though.

I realized the first scene, with Robin Penn Wright, was a single shot (brilliant, I might add), but then I didn't notice they were all that way until the third or fourth segment.

the very first scene in the jail.

I watched the first one in jail without catching it. Then I looked up the movie online and saw that information. So I don't know how long it would have taken! I can see how the Samantha scene would be more noticeable than others given the tight quarters. OTOH the way the camera did not follow Holly into the yard but observed her from a distance might have been a giveaway too. I'll never know...

Immediately.

I did not catch it during the first prison sequence. But somewhere during the second one, as they were cruising around the shopping mall, I asked myself: is it all in one take? And was the first one also in one take? OK, I see what they are trying to do. Quite clever.